Propeller

ABSTRACT

A PROPELLER OF THE MARINE SCREW TYPE HAVING A MAIN BLADE AND AN AUXILIARY BLADE LOCATED AT THE DISCHARGE END OF THE MAIN BLADE, SAID BLADES HAVING A SLOT RUNNING THEREBETWEEN AT THE TRAILING EDGE OF THE MAIN PROPELLER BLADE. THE WIDTH OF THE SLOT IN CROSS SECTIONAL AREA REDUCES ITS SIZE FROM THE PRESSURE SIDE OF THE BLADE TOWARDS THE SUCTION SIDE OF THE BLADE TO CREATE A THROTTLE EFFECT RESULTING IN AN INCREASE IN WATER FLOW VELOCITY THROUGH THE SLOT AND A REDUCTION OF THE PRESSURE IN THE SUCTION SIDE OF THE PROPELLER. THE STRUCTURE SO PRESENTED REDUCES CAVITATION   AND IMPROVES PERFORMANCE OF THE PROPELLER BY REDUCING TURBULENCE ON THE SUCTION SIDE OF THE PROPELLER BLADE.

Sept. 20, 1971 H. MEHus 3,606,519

PROPELLER Filed Jan. 22, 1969 INVENTOR BY f/AVMM United States PatentOffice 3,606,579 PROPELLER Henry Mehus, Kampens plass 12, Stavanger,Norway Filed Jan. 22, 1969, Ser. No. 792,972 Int. Cl. B63h 1/26 U.S. Cl.416-200 1 Claim ABSTRACT F THE DISCLOSURE tion side of the blade tocreate a throttle effect resulting in an increase in water tlow velocitythrough the slot and a reduction of the pressure in the suction side ofthe propeller. The structure so presented reduces cavitation andimproves performance of the propeller by reducing turbulence on thesuction side of the propeller blade.

This invention relates to propellers, particularly marine screws, butalso propellers for fans and the like, having two or more blades.

The primary object of the invention is to provide a propeller having ahigh efficiency, and more particularly the invention relates to apropeller wherein the main blade is provided with an auxiliary bladelocated at the discharge edge of the main blade when going forward, andthe novel features according to the present invention consist in thefollowing: that in an arbitrary axis parallel cylinder section throughthe blades the pitch on the blades is dened by helical lines through theterminal points of the longitudinal center lines of these sections, andthat the helical lines through the terminal points of the cylindersections of the auxiliary blade at the same radius have the same or alarger pitch than the helical lines of the main blade, and that thehelical lines of the auxiliary blade are located abaft of the helicallines of the main blade relative to the forward speed of the vessel.

The number of such pair of blades (main and auxiliary blade) may varyfrom two to any proper number.

The slot between the main blade and the auxiliary blade serves thefollowing purpose: When the propeller rotates, water (air, gas or thelike) will be urged in the direction of rotation along the pressure sideof the main blade and through the slot, which according to the equationof Bernoulli create an under-diminished pressure at the discharge edgeof the main blade, whereby the water flow at Ythe suction side of themain blade is prevented from loosing. Thereby the common undesiredturbulence on the suction side of the propeller blade is avoided.

The area of `the auxiliary blade is maximum half of the area of the mainblade.

The main blade and the auxiliary blade may be formed in one singlepiece, the blades being separated by a slot sloping astern and beinglimited by a por-tion of the pressure side of the main blade at itsdischarge edge and a portion of the suction side of the auxiliary bladeat its inlet edge, when the Vessel is going forward, corresponding tothe direction of flow of the Water.

In some instances it may be advantageous to arrange the main blade andthe auxiliary blade with a forwardly directed cast, and the auxiliaryblade may be revolving.

The propeller according to the invention will be further described byway of example in connection with the accompanying drawings, in which:

FIG. 1 illustrates the propeller, seen in the forward direction of thevessel, i.e. from the end of the hub;

FIG. 2 is a displayed cylinder section along line II-II 3,606,579Patented Sept. 20, 1971 in FI-G. 1, illustrating a main blade and anauxiliary blade, and indicating the pitchs helical lines and a,respectively;

FIG. 3 is a longitudinal sectional view through the hub and the pair ofblades along the lines IIIa-IIIa and IIIb-IIIb in FIG. 1;

FIG. 4 is a view similar to FIG. 2, but illustrating a modifiedembodiment, in which the main blade and the auxiliary blade is made inone single piece.

In the drawings the reference letter f (FIGS. 1 and 2) indicates theforward direction of the vessel, While d is indicating the rotationdirection of the propeller.

Each of the two blades (main blades) 1 of a propeller is provided withan auxiliary blade 2 located at the discharge edge of the associatedmain blade 1, assuming the -vessel is moving forward. In an arbitraryaxis parallel cylinder section, e.g. II-II in FIG. 1, through thepropeller blades 1, 2 the pitch on the blades is dened by helical linesthrough the terminal points of these sections longitudinal center lines.The helical lines through the terminal points of the cylinder sectionsof the auxiliary blade 2 (see FIG. 2) at the same radius have according-to lFIG. 2 a larger pitch than the helical lines of the main blade 1;this being illustrated on the drawing by the fact that a is larger thanThe helical lines through the terminal points of the center line of thecylinder sections of the auxiliary blade 2 may at the same radius beequal to those of the main blade with respect to the pitch, confer FIG.4 in which the main blade 1" and the auxiliary blade 2' are made in onesingle piece, a slot 4 being provided in order to separate the blades. Aplate piece 5 is welded to the main blade 1" in order to overlap theauxiliary blade 2' at the slot opening.

The helical lines of the auxiliary blade are located abaft of thehelical lines of the main blade 1 by forward motion of the vessel.

On the drawings the reference numeral 3 indicates the hub and 1' theinlet edge of the main blade by going forward. The slot between the mainblade and the auxiliary blade is 4 and 4', respectively.

Preliminary experiments have shown that very good results were obtainedwhen the slot 4 or 4' had a width in the axial direction ofapproximately 0.06-0.09 times that of the main blade by 0.6 of theradius of the main blade.

If desired, the auxiliary blade can be made revolving (not shown), whichcan be achieved by any of a number of known methods. In the shownembodiment the auxiliary blade 2, 2 and the main blade 1, 1" have castforwardly (see FIG. 3).

What I claim is:

1. A propeller suitable for use as a marine screw having a hub and amain blade and an auxiliary blade on said hub, said main blade and saidauxiliary blade both slope forwardly with respect to the forwarddirection of travel of a vessel propelled by said propeller, saidauxiliary blade having a maximum of one-half the area of the main blade,said auxiliary blade being disposed adjacent the discharge end of themain blade and overlapping the trailing edge of the main blade with thepressure side of the main blade facing the suction side of the auxiliaryblade, whereby a slot is formed between said auxiliary blade and thetrailing edge of said main blade, the auxiliary blade and said mainblade being so proportioned that the slot has a length of about 0.6times the radius of the main blade and a width of 0.06 to 0.09 times thewidth of the main blade, and the pitch angle of said auxiliary bladebeing at least equal to the pitch angle of said main blade.

(References on following page) 4 References Cited FOREIGN PATENTS UNITEDSTATES PATENTS 68,480 1941 Czechoslovakia 416-231 176,842 3/ 1922 GreatBritain 416-231 lgfg @ggg 851,524 10/1960 Great Britain 416-231 Faber 57/1936 Vargas 170-172 3/1939 Baker 170 172 EVERETTE A. POWELL, JR.,Prxmaly Exammer 5/1939 Barnett 170-172 XR Tl-.Smel 10 CL l l 4/ 1966Saunders 416-231 6/1968 Grebe 416-200X

